The document discusses powder metallurgy, which involves producing metal parts from metal powders. The basic steps are powder production, blending/mixing, powder consolidation like die pressing, and sintering. Powder metallurgy allows production of parts from metals with high melting points or that are difficult to machine, and is commonly used for automotive applications. It provides good dimensional accuracy and control over porosity and properties.

1. ME 355 Sp’06 W. Li 1
Powder Metallurgy (P/M)
• Competitive with processes such as
casting, forging, and machining.
• Used when
• melting point is too high (W, Mo).
• reaction occurs at melting (Zr).
• too hard to machine.
• very large quantity.
• Near 70% of the P/M part production
is for automotive applications.
• Good dimensional accuracy.
• Controllable porosity.
• Size range from tiny balls for ball-
point pens to parts weighing 100 lb.
Most are around 5 lb.

2. ME 355 Sp’06 W. Li 2
Basic Steps In Powder Metallurgy
• Powder Production
• Blending or Mixing
• Powder Consolidation
• Sintering
• Finishing

3. ME 355 Sp’06 W. Li 3
1. Powder Production
(a) (b) (c)
(a) Water or gas atomization; (b) Centrifugal atomization; (c) Rotating electrode
• Many methods: extraction from compounds, deposition,
atomization, fiber production, mechanical powder
production, etc.
• Atomization is the dominant process

4. ME 355 Sp’06 W. Li 4
Characterization of Powders
Size of powders 0.1 um – 1 mm
Sieve size quoted as mesh number
Particle D = 15/mesh number (mm)
325 mesh 45 um

5. ME 355 Sp’06 W. Li 5
2. Blending or Mixing
• Blending a coarser fraction with a finer fraction ensures
that the interstices between large particles will be filled out.
• Powders of different metals and other materials may be
mixed in order to impart special physical and mechanical
properties through metallic alloying.
• Lubricants may be mixed to improve the powders’ flow
characteristics.
• Binders such as wax or thermoplastic polymers are added
to improve green strength.
• Sintering aids are added to accelerate densification on
heating.

6. ME 355 Sp’06 W. Li 6
3. Powder Consolidation
Die pressing
• Cold compaction with 100 – 900
MPa to produce a “Green body”.
• Die pressing
• Cold isostatic pressing
• Rolling
• Gravity
• Injection Molding small, complex
parts.

7. ME 355 Sp’06 W. Li 7
Friction problem in cold compaction
• The effectiveness of pressing with a single-acting punch is
limited. Wall friction opposes compaction.
• The pressure tapers off rapidly and density diminishes away
from the punch.
• Floating container and two counteracting punches help
alleviate the problem.

8. ME 355 Sp’06 W. Li 8
4. Sintering
• Parts are heated to 0.7~0.9 Tm.
• Transforms compacted mechanical
bonds to much stronger metallic
bonds.
• Shrinkage always occurs:
sintered
green
green
sintered
V
V
shrinkage
Vol
ρ
ρ
=
=
_
3
/
1
_ 







=
sintered
green
shrinkage
Linear
ρ
ρ

9. ME 355 Sp’06 W. Li 9
5. Finishing
• The porosity of a fully sintered part is still significant (4-15%).
• Density is often kept intentionally low to preserve
interconnected porosity for bearings, filters, acoustic barriers,
and battery electrodes.
• However, to improve properties, finishing processes are
needed:
• Cold restriking, resintering, and heat treatment.
• Impregnation of heated oil.
• Infiltration with metal (e.g., Cu for ferrous parts).
• Machining to tighter tolerance.

10. ME 355 Sp’06 W. Li 10
Special Process: Hot compaction
• Advantages can be gained by combining consolidation and
sintering,
• High pressure is applied at the sintering temperature to bring
the particles together and thus accelerate sintering.
• Methods include
• Hot pressing
• Spark sintering
• Hot isostatic pressing (HIP)
• Hot rolling and extrusion
• Hot forging of powder preform
• Spray deposition

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Process Capabilities
Con’tional HIP Injection
Molding (IM)
Precision IM Preform
Forging
Metal All All (SA,
SS)
All (Steel, SS) All Steel, SA
Surface detail B B-C B A A
Mass, kg 0.01-5(30) 0.1-10
10-7000 (e)
0.01-0.2 0.005-0.2 0.1-3
Min. section, mm 1.5 1 0.1 3
Min. core diam. mm 4-6 1 0.2 5
Tolerance +/-% 0.1 2 0.3 0.1 0.25
Throughput (pc/h) 100-1000 5-20 100-2000 100-2000 200-2000
Min. quantity 1000-50,000 1-100 10,000 10,000 100,000
Eq. Cost B-C A A-B A-B A-B
A: highest, B: median, C: lowest

12. ME 355 Sp’06 W. Li 12
Design Aspects
(a) Length to thickness ratio limited to 2-4; (b) Steps limited to avoid density variation; (c) Radii
provided to extend die life, sleeves greater than 1 mm, through hole greater than 5 mm; (d) Feather-
edged punches with flat face; (e) Internal cavity requires a draft; (f) Sharp corner should be avoided;
(g) Large wall thickness difference should be avoided; (h) Wall thickness should be larger than 1 mm.

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Advantages and Disadvantages of P/M
• Virtually unlimited choice of alloys, composites, and
associated properties.
• Refractory materials are popular by this process.
• Controlled porosity for self lubrication or filtration uses.
• Can be very economical at large run sizes (100,000 parts).
• Long term reliability through close control of dimensions
and physical properties.
• Very good material utilization.
• Limited part size and complexity
• High cost of powder material.
• High cost of tooling.
• Less strong parts than wrought ones.
• Less well known process.